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The musician, 75, opened up about the loss in a statement to PEOPLE after it was revealed that Joanna, 85, died of thyroid cancer on Wednesday and Lucy, 82, died of metastatic breast cancer on Thursday.
"I am filled with sorrow to speak about the passing of Joanna and Lucy Simon. Their loss will be long and haunting," Simon told PEOPLE in a statement. "As sad as this day is, it's impossible to mourn them without celebrating their incredible lives that they lived. We were three sisters who not only took turns blazing trails and marking courses for one another, we were each other's secret shares. The co-keepers of each other's memories."
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The deaths of Lucy, who was a Tony Award-nominated Broadway composer, and Joanna, who was an opera singer, were confirmed to Deadline on Friday. Their younger brother Peter Simon, a longtime photographer on Martha's Vineyard, died in 2018 at 71 after he was diagnosed with lung cancer.
"I have no words to explain the feeling of suddenly being the only remaining direct offspring of Richard and Andrea Simon," Simon said, adding that her sisters "touched everyone they knew and those of us they've left behind will be lucky and honored to carry their memories forward."
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Carly Simon rates our affection and condolences—for her sister Joanna (an international opera star) died on Tuesday. A day later, her younger sister Lucy, (who composed a Broadway musical) died of cancer as well. Carly is one of the most decent artists for whom I’ve arranged. pic.twitter.com/4LKvU7MoGX
— Van Dyke Parks (@thevandykeparks) October 22, 2022
Musician Van Dyke Parks, a collaborator of Simon's, shared condolences to Twitter following the news, calling the "You're So Vain" singer "one of the most decent artists for whom I've arranged."
Lucy and Carly were early collaborators in the 1960s when she formed the iconic folk duo, The Simon Sisters, with Carly. Together, the pair shared the song "Wynken, Blynken & Nod" in 1964, before Lucy went to nursing school and married David Levine in 1967. Simon and Levine share two children together, Jamie and Julie.
After producing two Grammy-winning children's albums in the '80s — In Harmony and In Harmony 2 — Lucy eventually became the third female composer on Broadway, having earned a Tony nomination in 1991 for her The Secret Garden score.
Joanna debuted in Mozart's "The Marriage of Figaro" at the New York City Opera in 1962, per Playbill, and performed at the Seattle Opera and with the New York Philharmonic, the Vienna Philharmonic and the Pittsburgh Symphony Orchestra during her career.